A large number of compounds which have an inhibitory effect on cGMP PD esterases are disclosed in the literature.
Thus, EP-A1 0201 188 describes pyrazolo4,3-d!-pyrimidin-7-ones as adenosine receptor antagonists and PDE inhibitors which can be used for the treatment of disorders of the coronary vessels of the heart associated with heart failure or cardiac insufficiency. However, this publication gives no examples of these compounds, nor are they particularly effective PDE inhibitors, in particular for cGMP PDE.
WO-A1 93/06104 describes substitutedpyrazolo4,3-d!pyrimidin-7-ones with an inhibitory specificity for cGMP PD esterases by comparison with that for cAMP PD esterases which is improved by comparison with the class of compounds disclosed in the aforementioned publication. The selectivity of these compounds for the other phosphodiesterases I, II and III is, however, not mentioned in this publication.
However, the simultaneous inhibitory effect of a compound on the other phosphodiesterases is of great importance to their utility because when there is a simultaneous inhibitory effect on other esterases apart from cGMP phosphodiesterase (PDE V) a whole range of unwanted side effects may emerge when it is used as medicament.